A fully-automatic firearm fires continuously as long as the trigger is depressed, as long as the ammunition is fed into the chamber. A semi-automatic firearm, on the other hand, only fires a shot per trigger pull, and cycles to chamber new rounds. This means a semi-automatic firearm only fires one round per trigger pull, and this makes it more convenient for hunting and sport shooting.
In most developed countries, fully-automatic firearms are reserved for the military or police, and may be subject to tighter regulation than other types of firearms. In the United States, fully-automatic firearms are strictly regulated by the National Firearms Act of 1934 and the Firearm Owners Protection Act of 1986. The latter also closed the machine gun registry, meaning that only previously registered automatic weapons can be bought and sold.